This invention relates to a high-efficiency thermal group comprising a boiler and a clear blue flame burner.
The operation efficiency of a thermal group largely depends on the thermal characteristics and the efficiency of the burner, as well as on the rate of heat exchange between hot flue gases and the water to be heated in the boiler.
As is known, in liquid-fuel firing burners, such as oil firing burners, fuel must be supplied under pressure for being finely sprayed from a suitable atomizer. It may frequently occur that, after repeated cyclical burner ignition and blow-out operations, relatively small amounts of fuel are still fed into the burner at the time when the ignition electrode(s) is (are) turned off. Such fuel amounts, besides being wasted because they remain virtually unburned, tend to build up inside the burner and in time to foul and trigger the formation of sooty deposits on the inner walls of the burner combustion chamber, which results in unburned products being included in the flue gases and thus in the need of servicing the plant.
Moreover, and in particular when the burner is cyclically started, it may occur that the liquid fuel supplied to it is overheated along its feed-in path to the atomizer inside the burner. Thus, a sharp local temperature increase is caused due to the burner inner walls being kept hot inside the boiler between successive cycles. Fuel heating results in sudden expansion of the jet issuing from the atomizer. Accordingly, the flame stability and consistency may be deteriorated which leads to incomplete combustion and poor efficiency.